Some comments.

> and my privacy settings (i.e. ‘hide notes tagged #NSFW’)

It should be noted that both tags and the "sensitive content" flag (NIP-36) are set arbitrarily by the poster.
There are no global "social" standards in the Nostr community and there never will be. If there were, there would be none to actually enforce them.
So do keep that in mind when trying to avoid certain kinds of content: you can get a decent heuristic at best.

> The variance in number of Followers

Look up NIP-02.
It's trivial to fetch what users an account follows, but when fetching the accounts a certain user is followed by, the client need to receive each one of them individually, and count them.
It's not dissimilar to fetching all replies to a post.

> In general, all clients use a very simple algorithm to populate your “home” feed

I don't think it's the case for all clients. Also, new strategies can be designed.
Any client can do what it wants and users can use whatever client they want.

> In this way, these clients can almost mimic current social app functionality like you might see on TikTok or Spotify or Medium, pulling only from Nostr data that meet certain note-type criteria.

It's worth noting that, while long-form notes are Nostr-native through NIP-23, music, videos and images are usually simply stored as links, typically to old-style centralized services.
There is still an advantage in sharing links trough a censorship-resistant system, but it's still worth noting.

> The other interesting thing about relay operators is that they are the only ones in the Nostr-verse that see all notes’ IP addresses. This was designed to help flag spammers and bots.

No, it wasn't.
This is simply how the Internet works.
When your device communicates to a relay, the relay necessarily knows your IP address because it couldn't send you a response otherwise.
It isn't a decision by Nostr authors that relays see your IP address, it's just how the network works when you connect to a server.

> If my TikTok account gets banned, I have no recourse to get that data back

This isn't false of centralized platforms, but, just as a side note.
If the platform you are using is GDPR-compliant, you will be able to get a copy of all data about you which they have, as long as you are a user.